SHRUB GROWTH AND DEMOGRAPHY IN ARID KAROO, SOUTH-AFRICA - INFERENCE FROM WOOD RINGS

Pteronia pallens (Asteraceae) produced annual growth rings, the width of which were influenced by water availability, particularly in the wi nter growing season. Ring widths (mean 0.83mm, S.D. 0.46mm) are within the range reported for other desert shrubs. Field measurements of bas al diameter were significantly correlated with the number of growth ri ngs, but accuracy of age estimates was limited by the longitudinal spl itting of the stems. Longevity estimates from basal diameters suggest that P. pallens can live for 150 years. Age class frequency distributi ons of P. pallens at the study sites showed two peaks over the period 1920 to 1990. Rainfall explained only 33% of the variation in recruitm ent. Other factors, such as the reduction of competition by drought or grazing, may have had a greater influence on recruitment patterns. (C ) 1997 Academic Press Limited.